Some part of the armature is not visible anymore thought the mesh in weight paint mode
Mate. You have X-Ray turned on for both the Armature and the body, so it's the same as if you did not have X-Ray turned on for either of them. You show edit mode with wireframe on, that's why you see everything. If you went to Solid view, it would look exactly the same as in Weight Paint. If you want to see bones through the body, you have to turn X-Ray on for the Armature, but not on for the body and if you want to see body always on top, you have to turn X-Ray on for the body, but not on for the Armature.